User equipments (UEs) in a universal telecommunications radio access network (UTRAN) are typically in either of two modes: Idle or Connected. Based on UE mobility and activity while in connected mode, the UTRAN can direct the UE to transition between a number of sub-states, such as cell paging channel (Cell_PCH), UTRAN Registration Area Paging Channel (URA_PCH), cell forward access channel (Cell_FACH), and Cell_DCH. This is typically accomplished through a network based reconfiguration procedure or as a result of a cell update procedure. The latter is initiated by the UE to tell the network about its current location. The Cell_DCH state is characterized by dedicated channels in both the uplink and the downlink. On the UE side, this corresponds to continuous transmission and reception and can be demanding on user power requirements. The Cell_FACH state does not use dedicated channels and thus allows better power consumption, at the expense of a lower uplink and downlink throughput.
Recent work by the standardization bodies has identified the possibility of using High-Speed Downlink Packet Access (HSDPA) in Cell_FACH and Cell/URA_PCH. HSDPA is a feature that was introduced in Release 5 of the Third Generation Partnership Project (3GPP) specifications to operate in Cell_DCH. HSDPA tries to make better use of the downlink shared capacity by using concepts such as Adaptive Modulation and Coding (AMC), retransmissions using a Hybrid-ARQ (HARQ) scheme, and Node B scheduling—all operating at a very fast rate. Packet data units (PDUs) are combined by the HARQ, and subsequently stored in a reordering queue to deal with possible out-of-order reception. Downlink transmissions are addressed to a UE via an HS-DSCH Radio Network Identifier (H-RNTI).
It is assumed that if the UE supports HSDPA in Release 7, then it also supports HSDPA in CELL_FACH and in CELL/URA_PCH. HS-DSCH reception in CELL_FACH can be configured without HS-DSCH reception in CELL_PCH and URA_PCH. High speed downlink shared channel (HS-DSCH) reception in CELL_PCH and URA_PCH without the support of HS-DSCH reception in CELL_FACH is not supported. The UE support for these features is signaled to the network. It should be understood that the embodiments presented can be extended to cases where the support for HSDPA in CELL_FACH and/or CELL_PCH/URA_PCH can be individually signaled to the network.
On the other hand, the network signals its support for enhanced CELL_FACH via the System Information Block (SIB5/5bis). Two new information elements (IEs) have been introduced: “HS-DSCH common system information”—indicating the HSDPA reception is supported for CELL_FACH state; and “HS-DSCH paging system information”—indicating that HSDPA reception is supported for CELL/URA_PCH state.
To indicate whether HS-DSCH reception is ongoing in CELL_FACH, two new Boolean variables have been added: HS_DSCH_RECEPTION_CELL_FACH_STATE: If TRUE indicates that HS_DSCH reception in CELL_FACH is ongoing; and HS_DSCH_RECEPTION_OF_CCCH_ENABLED: If TRUE indicates that HS-DSCH reception is enabled for CCCH. This variable is set to TRUE when the UE is using a common H-RNTI to receive HSDPA traffic, and is set to FALSE when the UE is not.
A UE is assigned a common H-RNTI to receive traffic when it has not been assigned a dedicated H-RNTI. Three such situations are as follows:                1) UE sends a Radio Resource Control (RRC) CONNECTION REQUEST message (and UE is waiting for an RRC CONNECTION SETUP response from the network).        2) UE sends a CELL UPDATE message and is waiting for a CELL UPDATE CONFIRM response from the network.        3) UE sends a URA UPDATE message and is waiting for a URA UPDATE CONFIRM response from the network.        
No new variable has been proposed for CELL/URA_PCH HS-DSCH reception indication. When in CELL/URA_PCH, and if the IE “HS-DSCH paging system information” is broadcast, the UE sets up HSDPA reception. In some cases, a UE will no longer be able to continue reception of high speed PDUs, (e.g., as a result of a hard handover, cell reselection, radio link failure, and the like). In these cases, the MAC should be reset. The reset procedure allows the UE to forward all PDUs in the reordering queues up to higher layers, and to re-initialize all high speed state variables.
In 3GPP Release 6, HSDPA was only supported in CELL_DCH. As a result, MAC resets, (e.g., a mac-hs reset) were performed under the following conditions: the UE underwent a radio link failure, the UE experienced an RLC unrecoverable error, or the UE was ordered to transition to a state where HSDPA was not supported (all states except CELL_DCH).
In Release 7, as currently defined, a UE may be required to perform a MAC reset in the following states: CELL_DCH, CELL_FACH, CELL/URA_PCH. In addition to the conditions specified above, (i.e., that apply to a UE in CELL_DCH), the UE is required to perform a MAC reset after ALL cell reselections. Currently this is only done when the WTRU with a dedicated H-RNTI performs a cell reselection. There are a number of scenarios where this reset is not performed, resulting in possible reordering errors.
Transitions to/from IDLE mode have also been impacted by the introduction of Enhanced CELL_FACH. If a Release 7 UE supports HSDPA reception in CELL_FACH state, this UE also supports limited HSDPA reception while in IDLE mode; in particular after a UE has issued an RRC CONNECTION REQUEST, and is waiting for an RRC CONNECTION SETUP message from the network. Three issues have been identified:
1) If the UE has begun HSDPA reception while in IDLE mode (after issuing a RRC CONNECTION SETUP message), any cell reselections should result in a MAC reset.
2) If an RRC connection procedure is aborted, the UE should clear all its HSDPA resources.
3) While in IDLE mode, a UE may cell reselect from a cell that supports Enhanced CELL_FACH to one that does not, and vice versa. If the UE has initiated an RRC connection procedure, two issues may need to be addressed. First, for a Release 6 to a Release 7 transition, the UE is required to setup the HSDPA resources so that it can receive the RRC CONNECTION SETUP message on the HS-DSCH. Second, for a Release 7 to Release 6 transition, the UE should release all HSDPA resources, as no traffic is expected on the HS-DSCH.
Another new feature of Enhanced CELL_FACH is that the UE will be able to receive dedicated control messages while in CELL_PCH (over the DCCH). Accordingly, a UE may be asked to perform a reconfiguration, (e.g., radio bearer, transport channel, physical channel). Reconfiguration messages can also result in a state change.
In order to allow proper configuration of HSDPA resources the UE should properly manage the setting or clearing of the variable HS_DSCH_RECEPTION_OF_CCCH_ENABLED to ensure that it is only set to TRUE when the UE is using the common H-RNTI while in an enhanced Cell_FACH state. It should be set to FALSE in all other states. Lastly, cell reselections occurring during ongoing cell update or URA update procedures should behave similarly to cell reselections when these procedures are not ongoing.
It would therefore be beneficial to provide a method and apparatus for handling cell reselections and transitions to and from an enhanced CELL_FACH state.